Browsing by Author "Churchill, Steven E"
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Item Open Access A 3D Geometric Morphometric Investigation of Relatedness in the Modern Human, Chimpanzee, and Homo naledi Postcranial Skeleton(2023) Rossillo, Amanda NoelleStudies of skeletal variation form the basis of our understanding of our species’ history and diversity. This most commonly takes the form of comparative, between- species studies aimed at reconstructing phylogenetic relationships. However, studies of within-species variation can provide insights into relatedness at smaller scales, which can shed light on important microevolutionary processes and be used to identify closely related individuals in the absence of DNA. This dissertation assesses the relationship between genetic and skeletal variation within groups of related and unrelated Homo sapiens and Pan troglodytes, with the aim of better understanding the population sampled by the seemingly homogenous Homo naledi assemblage from the Dinaledi Chamber in Rising Star Cave, South Africa. The hypotheses tested were: 1) closely related individuals exhibit less skeletal variation compared to unrelated individuals, and 2) the Dinaledi assemblage exhibits less morphological variation than H. sapiens and P. troglodytes at the species level, more closely resembling a single population.
Skeletal variation within a subset of H. sapiens from the crypt of Christ Church in Spitalfields, London (17-19th centuries A.D) with documented genealogies and the Gombe population of P. t. schweinfurthii was compared to species-wide baselines and the H. naledi assemblage. The data consisted of 3D models of 556 postcranial elements (first metacarpal (Mc1), proximal femur, talus, calcaneus, and navicular) from 187 individuals that were generated from surface scanners or downloaded from MorphoSource.
This dissertation employed a relatively new 3D geometric morphometric workflow that captures the entire shape of an element through the use of an automated landmarking program and feature-aware registration process. Two hundred pseudolandmarks were automatically and optimally placed on each element. Following alignment, multiple univariate and multivariate statistical analyses were used to quantify shape variation within and between the three species, including distributions of Euclidean distances, Procrustes distances to the mean shapes, Principal Components Analyses (PCA), Between-Group PCA, and Discriminant Function Analyses. The coefficient of relationship was used to represent genetic distance between known genetic relatives within modern humans.
The results of the within-species analyses of skeletal variation support Hypothesis 1 in both modern humans and chimpanzees, though the signal of relatedness is differentially expressed within and across elements. In modern humans, the calcaneus can be used to distinguish known close relatives from distantly related and unrelated individuals. The navicular and femur were also found to be relatively good indicators of relatedness. Within chimpanzees, the talus is the most effective at distinguishing the Gombe population from the species-wide chimpanzee sample, followed by the calcaneus and femur. Within H. naledi, the talus varied the least while the navicular varied the most, though the high levels of variation found in the navicular and Mc1 are likely due to the state of preservation of these elements. The results of the interspecies analyses are more ambiguous. When considering the best preserved elements, the H. naledi talus varies the least within the three species, while the femur varies more than those of either H. sapiens or P. troglodytes at the species level. Hypothesis 2 is thus supported for the talus while rejected in the femur, suggesting that it cannot be rejected as a whole and that the patterns of homogeneity previously observed within H. naledi are more nuanced than previously recognized.
Item Open Access Evaluating morphometric body mass prediction equations with a juvenile human test sample: accuracy and applicability to small-bodied hominins.(Journal of human evolution, 2018-02) Walker, Christopher S; Yapuncich, Gabriel S; Sridhar, Shilpa; Cameron, Noël; Churchill, Steven EBody mass is an ecologically and biomechanically important variable in the study of hominin biology. Regression equations derived from recent human samples allow for the reasonable prediction of body mass of later, more human-like, and generally larger hominins from hip joint dimensions, but potential differences in hip biomechanics across hominin taxa render their use questionable with some earlier taxa (i.e., Australopithecus spp.). Morphometric prediction equations using stature and bi-iliac breadth avoid this problem, but their applicability to early hominins, some of which differ in both size and proportions from modern adult humans, has not been demonstrated. Here we use mean stature, bi-iliac breadth, and body mass from a global sample of human juveniles ranging in age from 6 to 12 years (n = 530 age- and sex-specific group annual means from 33 countries/regions) to evaluate the accuracy of several published morphometric prediction equations when applied to small humans. Though the body proportions of modern human juveniles likely differ from those of small-bodied early hominins, human juveniles (like fossil hominins) often differ in size and proportions from adult human reference samples and, accordingly, serve as a useful model for assessing the robustness of morphometric prediction equations. Morphometric equations based on adults systematically underpredict body mass in the youngest age groups and moderately overpredict body mass in the older groups, which fall in the body size range of adult Australopithecus (∼26-46 kg). Differences in body proportions, notably the ratio of lower limb length to stature, influence predictive accuracy. Ontogenetic changes in these body proportions likely influence the shift in prediction error (from under- to overprediction). However, because morphometric equations are reasonably accurate when applied to this juvenile test sample, we argue these equations may be used to predict body mass in small-bodied hominins, despite the potential for some error induced by differing body proportions and/or extrapolation beyond the original reference sample range.Item Open Access Evaluating the Hominin Scavenging Niche through Analysis of the Carcass-Processing Abilities of the Carnivore Guild(2008-08-08) Hartstone-Rose, AdamHumans are more carnivorous than other hominoids. It has been hypothesized that, during the evolution of this increased carnivory, hominins transitioned through a scavenging niche made viable by certain carnivoran taxa (especially sabertooths) that may have lacked the morphology necessary to fully utilize all parts of carcasses (e.g., marrow), therefore leaving an open niche in the form of high-quality scavengable remains available for hominins. In this dissertation, I examine the postcanine dentition of modern carnivorans, using quantifications of occlusal radii of curvature and intercuspid notches, and study the correlation of this morphology with carcass-processing behavior. I use these correlations to deduce the carcass-processing capabilities of the Plio-Pleistocene carnivores of South Africa (a guild for which we have a good appreciation of taxonomic diversity, and that existed at an important time during the evolution of our lineage - possibly the time that we transitioned into that guild), and compare these results with those of previous studies that relied on more conventional morphological measures.
Both radius of curvature and intercuspid notch data do a good job of separating taxa by dietary category, revealing subtle patterns including possible differences in the carcass-processing abilities of fossil and modern members of some extant species. Other strong trends confirm that the "hunting-hyena," Chasmaporthetes, was probably a hypercarnivore, and not a durophage like its modern confamilial taxa. Somewhat surprisingly, results do not support the hypothesis that sabertooth felids were more hypercarnivorous than modern felids. Furthermore, though the sympatric hypercarnivorous taxa were more numerous, so to were the durophageous taxa, with one taxon, Pachycrocuta, probably exceeding the durophageous capabilities of modern durophages.
As such, this dissertation shows no evidence that members of the paleo-carnivore guild were capable of producing higher quality scavengable carcasses than are modern carnivorans, and thus, based on these analyses of fossil carnivorans, it does not appear that high-quality scavengable remains were more available in the Plio-Pleistocene than there are today. Therefore, though there is clear evidence from other sources that hominins did scavenge at least occasionally, this dissertation does not support the hypothesis that there was an open niche consisting of high-quality scavengable remains.
Item Open Access Functional Integration of the Hominin Forelimb(2015) Macias, Marisa ElenaDuring the last six million years, humans shifted from a primarily arboreal lifestyle to a habitually bipedal, terrestrial lifestyle. Australopithecus had a significant bipedal component to its locomotion; whether suspensory and climbing behavior were also important has remained unclear. Morphological features of the forelimb have been linked to locomotor differences among primates, but the interpretation of human fossils has remained problematic.
This dissertation examined the total morphological pattern of the forelimb, specifically the functional integration of the musculature and joint systems. This approach employed both geometric morphometrics and a biomechanical modeling approach to studying how and how well the forelimb morphology of living suspensory and quadrupedal primates, as well as humans and fossil hominins, accommodate climbing and suspensory locomotion. Data collected with a microscribe 3-D digitizer on the scapula, humerus, radius, and ulna of Australopithecus sediba, Australopithecus afarensis, and Homo erectus were compared to a sample of Homo sapiens, Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus, Hylobates lar, and Macaca fuscicularis.
The hominin upper limb is a rich mosaic of primitive and derived traits. The blade of Australopithecus sediba, although appearing most similar to extant orangutans, is in fact functionally most similar to chimpanzees. The overall morphology of the australopith elbow joint appears most similar to Pan, as does the elbow joint of Homo erectus, suggesting that the modern human configuration happened more recently than 1.5 million years ago.
Au. afarensis and Au. sediba share important similarities, but are clearly distinct species. While their overall elbow joint shape is strikingly similar, the articular surface is not identical. Au. afarensis is more similar in this respect to Pan and Homo, while Au. sediba is more similar to extant taxa that spend substantially more time engaging in vertical climbing and suspensory behavior.
The results from this study support previous interpretations that not all australopiths across time were employing the same locomotor repertoire. While this study does not present unambiguous conclusions regarding early hominin arboreal locomotion, this study suggests that the morphology of the upper limb is varied, and caution must be taken when interpreting single skeletal elements in the hominin fossil record.
Item Open Access Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa.(eLife, 2015-09) Dirks, Paul HGM; Berger, Lee R; Roberts, Eric M; Kramers, Jan D; Hawks, John; Randolph-Quinney, Patrick S; Elliott, Marina; Musiba, Charles M; Churchill, Steven E; de Ruiter, Darryl J; Schmid, Peter; Backwell, Lucinda R; Belyanin, Georgy A; Boshoff, Pedro; Hunter, K Lindsay; Feuerriegel, Elen M; Gurtov, Alia; Harrison, James du G; Hunter, Rick; Kruger, Ashley; Morris, Hannah; Makhubela, Tebogo V; Peixotto, Becca; Tucker, StevenWe describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. The chamber was always in the dark zone, and not accessible to non-hominins. Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occurring during/after deposition. Hominins accumulated over time as older laminated mudstone units and sediment along the cave floor were eroded. Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date.Item Open Access Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.(eLife, 2015-09) Berger, Lee R; Hawks, John; de Ruiter, Darryl J; Churchill, Steven E; Schmid, Peter; Delezene, Lucas K; Kivell, Tracy L; Garvin, Heather M; Williams, Scott A; DeSilva, Jeremy M; Skinner, Matthew M; Musiba, Charles M; Cameron, Noel; Holliday, Trenton W; Harcourt-Smith, William; Ackermann, Rebecca R; Bastir, Markus; Bogin, Barry; Bolter, Debra; Brophy, Juliet; Cofran, Zachary D; Congdon, Kimberly A; Deane, Andrew S; Dembo, Mana; Drapeau, Michelle; Elliott, Marina C; Feuerriegel, Elen M; Garcia-Martinez, Daniel; Green, David J; Gurtov, Alia; Irish, Joel D; Kruger, Ashley; Laird, Myra F; Marchi, Damiano; Meyer, Marc R; Nalla, Shahed; Negash, Enquye W; Orr, Caley M; Radovcic, Davorka; Schroeder, Lauren; Scott, Jill E; Throckmorton, Zachary; Tocheri, Matthew W; VanSickle, Caroline; Walker, Christopher S; Wei, Pianpian; Zipfel, BernhardHomo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.Item Open Access Midfacial Morphology and Neandertal-Modern Human Interbreeding.(Biology, 2022-08-03) Churchill, Steven E; Keys, Kamryn; Ross, Ann HAncient DNA from, Neandertal and modern human fossils, and comparative morphological analyses of them, reveal a complex history of interbreeding between these lineages and the introgression of Neandertal genes into modern human genomes. Despite substantial increases in our knowledge of these events, the timing and geographic location of hybridization events remain unclear. Six measures of facial size and shape, from regional samples of Neandertals and early modern humans, were used in a multivariate exploratory analysis to try to identify regions in which early modern human facial morphology was more similar to that of Neandertals, which might thus represent regions of greater introgression of Neandertal genes. The results of canonical variates analysis and hierarchical cluster analysis suggest important affinities in facial morphology between both Middle and Upper Paleolithic early modern humans of the Near East with Neandertals, highlighting the importance of this region for interbreeding between the two lineages.Item Open Access Morphometric panel regression equations for predicting body mass in immature humans.(American journal of physical anthropology, 2018-05) Yapuncich, Gabriel S; Churchill, Steven E; Cameron, Noël; Walker, Christopher SOBJECTIVES:Predicting body mass is a frequent objective of several anthropological subdisciplines, but there are few published methods for predicting body mass in immature humans. Because most reference samples are composed of adults, predicting body mass outside the range of adults requires extrapolation, which may reduce the accuracy of predictions. Prediction equations developed from a sample of immature humans would reduce extrapolation for application to small-bodied target individuals, and should have utility in multiple predictive contexts. MATERIALS AND METHODS:Here, we present two novel body mass prediction equations derived from 3468 observations of stature and bi-iliac breadth from a large sample of immature humans (n = 173) collected in the Harpenden Growth Study. Prediction equations were generated using raw and natural log-transformed data and modeled using panel regression, which accounts for serial autocorrelation of longitudinal observations. Predictive accuracy was gauged with a global sample of human juveniles (n = 530 age- and sex-specific annual means) and compared to the performance of the adult morphometric prediction equation previously identified as most accurate for human juveniles. RESULTS:While the raw data panel equation is only slightly more accurate than the adult equation, the logged data panel equation generates very accurate body mass predictions across both sexes and all age classes of the test sample (mean absolute percentage prediction error = 2.47). DISCUSSION:The logged data panel equation should prove useful in archaeological, forensic, and paleontological contexts when predictor variables can be measured with confidence and are outside the range of modern adult humans.Item Open Access Ontogeny of Lower Limb Morphology and Proportions in the Dinaledi Hominins(2015) Walker, Christopher ScottThe discovery of hundreds of fossil hominin remains from the Dinaledi Chamber of Rising Star cave in South Africa included dozens of immature elements attributed to multiple individuals. Some of these elements are amongst the most complete in the Dinaledi assemblage, but have not yet been fully studied. Thorough examination of these immature remains is important because they can provide a more complete understanding of the morphology of the Dinaledi hominins, facilitate an assessment of morphological development in the assemblage, and allow for direct comparisons with other immature fossil hominins. This dissertation focuses on the most diagnostic specimens of the immature lower limb (with reference to the immature upper limb and the mature sample) from the site and utilizes a comparative approach examining developmental variation in the proximal femur and limb proportions of extinct and extant ape species to discern the ontogenetic basis of the adult Dinaledi hominin form.
The first portion of this dissertation addresses the development of proximal femoral shape in an ontogenetic series of femora from the Dinaledi hominins, modern humans, chimpanzees, and gorillas. Results indicate that the development of proximal diaphyseal shape and neck-shaft angle are conserved within Homininae, but that neck shape may develop differently in bipeds than non-bipeds. The absolute shape of the femoral neck, however, markedly differs between the Dinaledi sample and modern humans, with greater anteroposterior constriction of the neck in the former, potentially due to increased superioinferior loading of the region associated with differing locomotor kinematics between species.
The second portion of this dissertation investigates the relative proportions of the immature Dinaledi lower limb. To date, the only lower limb long bone preserving the entire diaphysis and an articular surface to be recovered from the chamber, is the immature tibia, U.W. 101-1070. The length of this specimen was evaluated relative to the size of the preserved joint surface in an ontogenetic context and was found to be relatively long compared to other fossil hominins and even modern humans. The humero-tibial proportions of the immature Dinaledi hominins were found to be outside of the range of chimpanzees and gorillas, but comparable to modern humans and the immature Homo erectus specimen KNM-ER 15000. Together, these findings demonstrate that, with respect to relative lower limb length, the Dinaledi hominins are highly derived.
The mixture of primitive (australopith-like) and derived (Homo-like) features of the Dinaledi hominins identified in this dissertation are consistent with other early work on the assemblage and imply that the Dinaledi chamber contains Plio-Pleistocene hominins. Given small brain and predicted body sizes for the Dinaledi hominins, the results presented here suggest that relative limb elongation may have occurred prior to increases in brain and body size during hominin evolution and that bipedal energetic efficiency may have been the primary locus of selection.
Item Open Access Small-bodied humans from Palau, Micronesia.(PLoS One, 2008-03-12) Berger, Lee R; Churchill, Steven E; De Klerk, Bonita; Quinn, Rhonda LUNLABELLED: Newly discovered fossil assemblages of small bodied Homo sapiens from Palau, Micronesia possess characters thought to be taxonomically primitive for the genus Homo. BACKGROUND: Recent surface collection and test excavation in limestone caves in the rock islands of Palau, Micronesia, has produced a sizeable sample of human skeletal remains dating roughly between 940-2890 cal ybp. PRINCIPLE FINDINGS: Preliminary analysis indicates that this material is important for two reasons. First, individuals from the older time horizons are small in body size even relative to "pygmoid" populations from Southeast Asia and Indonesia, and thus may represent a marked case of human insular dwarfism. Second, while possessing a number of derived features that align them with Homo sapiens, the human remains from Palau also exhibit several skeletal traits that are considered to be primitive for the genus Homo. SIGNIFICANCE: These features may be previously unrecognized developmental correlates of small body size and, if so, they may have important implications for interpreting the taxonomic affinities of fossil specimens of Homo.Item Open Access To the Sticking Point: The Effectiveness of Tip Cross-Sectional Area versus Perimeter in Identifying Potential Lithic Armatures.(2017-05-21) Grady, JacksonKilling prey from a distance using complex projectile weapons is a behavior unique to Homo sapiens. The archeological remnants of these weapons are mostly limited to their lithic points, as their organic components have decomposed. In order to distinguish these points from stones fashioned for other purposes and more accurately determine the advent of this advanced technology, researchers have primarily utilized a measurement known as tip cross-sectional area (TCSA). This metric was thought to be the most ballistically significant one available for this purpose based on studies of high velocity projectiles. Sisk and Shea (2011) hypothesized that tip cross-sectional perimeter (TCSP) is a more useful ballistic measurement when identifying low velocity projectiles such as arrows and darts. To test this idea, we designed and printed six arrowheads divided into pairs with either the same TCSA but different TCSP, or the same TCSP but different TCSA. Our results support the Sisk and Shea hypothesis that TCSP is a better predictor of a point’s penetration than TCSA. We also found that surface area, which is highly correlated to TCSP, may be the most useful ballistic measurement for low velocity projectiles. Utilizing TCSP and surface area, rather than TCSA, may allow archeologists and anthropologists to more accurately categorize points found in archeological sites prior to 40ka, a watershed moment in the development of modern human behaviors and population growth. If projectile weapons are identified prior to 40ka, their development may have served as a catalyst in the early cognitive evolution of man.